Protection of cellulose against heat aging



sept. 1, 1953 H. M. BucKwALTER 2,650,891

PROTECTION OF CELLULOSE AGAINST HEAT AGING Filed April 13, 1951 20 Gyz m4n/wr af @Wa/v //Pf wea O l I I I I l l l I I oz46a|or2|4|6|eao CdA/Cf/V/'A//VF 7Ff47//V6 46E/V7', 5) W/6'//7 BY M4 Patented Sept. 1, 1953 PROTECTION OF CELLULOSE AGAINST HEAT AGING Howard M. Buckwalter, Detroit, Mich., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application April 13, 1951, Serial No. 220,946

17 Claims.

This invention relates to the protection of cellulose against heat aging, and more particularly it relates to a method of preventing the progressive irreversible loss of strength which occurs in cellulose when it is subjected to elevated temperatures for a prolonged period of timeas well as to improved cellulose articles produced by such treatment.

Ordinarily, when cellulose is subjected to elevated temperature, e. g., temperatures in excess of about 125 C., there occurs a slow but progressive unfavorable pyrolytic reaction which results in the gradual loss of desirable physical properties, especially tensile strength. This thermal deterioration has in the past placed a definite limitation on the length of service that could be expected from cellulose articles at elevated temperatures. The problem has been particularly acute in those applications Where cellulose in the form of fibers has been employed as reinforcement for rubber articles, such as pneumatic tires, steam hose, power transmission belts, conveyor belts, etc. These articles are commonly exposed to elevated temperature in use, either because they are subjected to external heating, or because they generate heat within themselves by reason of repeated rapid flexing, as in the case of pneumatic tires. The gradual thermal degradation of the cellulose fiber reinforcement in such articles leads eventually to breakage of the reinforcement, with consequent failure of the article. This deteriorating action of prolonged heating on cellulose is a principal cause of failure of such articles as pneumatic tires and steam hose.

Accordingly, it is a principal object of the present invention to provide a method for protecting cellulose, especially cellulose in the form of ber, such as cotton or rayon strands, yarns, cords or fabric, from thermal degradation. Another object is the provision of articles of manufacture embodying cellulose reinforcement protected against deterioration by heat aging. It is still another object of the invention to provide improved cellulose bers themselves, Whether unstranded, stranded, or in the form of fabric, and especially to provide vulcanized rubber articles reinforced with such cellulose bers, such as pneumatic tire casings reinforced therewith. The foregoing objects, and additional objects and advantages of the invention, will more fully hereinafter appear.

1n the accompanying drawing:

Fig. l is a graph showing the tensile strength of rayon tire cord treated in accordance with the invention, plotted as a function of the concentration of the treating agent; and

Fig. 2 is a similar graph for cotton tire cord.

The invention contemplates the protection of cellulose against deterioration by heat aging by incorporating therein a Water soluble 2,2'di amincdialkylsulflde. I have unexpectedly discovered that the water soluble 2,2diarninodi alkylsullides are highly eiective for imparting to cellulose the ability to withstand degradation by the action of heat over extended periods of time. Y

In practicing the invention, the 2,2-diamino dialkylsulde may be applied to the cellulose in any convenient manner, for example, by immersing the cellulose to be treated in a solutionI usually an aqueous solution, of the 2,2diamino dialkylsulde for a period of time sufficient for the cellulose to imbibe the 2,2-diaminodialkyl sulfide, and to become substantially impregnated therewith.

The cellulose is usually employed in the form of fiber, such as ordinary grey cotton fiber, although the process of the invention may be employed with equal advantage with the various regenerated cellulose bers, such as viscose rayon, or with regenerated cellulose in non-fibrous form, such as in sheet form. The invention is applicable to native cellulose bers in general, such as ax, hemp, etc., as well as to scoured, bleached and mercerized cotton, or to fibers treated with alkali-metal abietate or congoplate as disclosed in U. S. Patents 2,297,536 and 2,422,078 respectively. In place of immersing the cellulose in the treating solution, I may incorporate the 2,2di aminodialkylsulde in the cellulose in any other suitable manner, such as by spraying or brushing.

The 2,2-diaminodialkylsulfldes which I employ in my invention are those which are water soluble and which are therefore readily imbibed by the hydrophilic cellulose. The 2,2'diamino dialkylsuldes having the desired Water solubility are those in which the alkyl groups are lower alkyl groups, viz., alkyl groups having six carbon atoms or less. 2,2diaminoethylsulde is preferred because of its ready solubility in water, ,its ease of preparation, its economy, and its effectiveness. This compound has the structural formula and is 'a water soluble liquid having a boiling point of 23h-33 C. It may be prepared, for exL ample, by reacting ethyleneimine with hydrogen sulde (Gabriel and Eschenbach; Ber. 30 2497). The 2,2'-diaminodialkylsuldes having higher alkyl groups than 2,2diaminodiethy1sulde, such as 2,2-diaminodihexy1sulde, are less preferred. q

The treatment with th 2,2'dia1inodialkyl sulfide may be carried out at room temperature if desired, or at elevated temperatures, for example, up to and including the boiling point of the aqueous or other solution of the treating chemical. 'I he time of contact between the cellulbsematerial andthe treating chemical should be sumti-ent to permitsubstanuai penetration of the fiber. Usually treatments of seconds to 2 minutes duration are adequate for this purpose.

When the treating chemical is employed as a solution the concentration of the treating chemical is generally preferably within the range of from about 2% to about 10% by weight, although remarkable improvement in heat resistance of the cellulose is frequently observed when the concentration of the 2,2'-diaminodialkylsulfide is as little as 0.2% in the treating Solution. If desired, more 'concentrated solutions may be employed, e. g., a 20% solution; or an even more concentrated solution, although there is ordinarily 'only minor advantage in ,using solutions appieciably more concentrated than about 5 or When the cellulose is contacted with such a solution ofthe treating chemical the treating chemical diiuses into and is imbibed within the cellulose, and is thereby deposited throughout the interior structure i the cellulose in molecular eontact with the cellulose molecules.

In order to obtain the b enets of the treatriijeht ef th invent-munisessentiai that the 2,2'diarinodialkylsulde remain in the cellulose and be actually present as such in the cellulose at the time the cellulose is subjected to the heating which would ordinarily cause deterioration. In order to impart eiective protection against thermal dgradation of the cellulose, only a minor amount of the treating agent need be present therein. For example, 2,2diamn'odi ethyl's'ulde present in amountof as little as 1% by weight of the treated cellulose produces a definite improvement. Typically, thetreatment according t'o the invention will result in the deposition oi. from about 1% vto 6% by weight of the treating chemical, based on the weight of the Ytreated cellulose, although greater amounts of the treating chemical are ordinarlywithout deleteriousv eie'ct on the cellulose, and there is no critical limitation on the upper concentration of the treating chemical which may be present in the cellulose. I

l The following exampleswill illustrate the Dractice of rny intention in more detail.

4 EXAMPLE 1 Rayon tire cords were immersed in a boiling aqueous solution of 2,2'diaminodiethylsuliide of various concentrations for a period of 2 minutes. 5 as a result of which the cord imbibed definite amounts of 2,2 diaminodiethylsulde. The cords were then removed from the solution, and the excess solution was allowed to drain off. The cords were then dried at 110 C. The cords were then conditioned to contain 10-11% moisture and thereafter aged by heating in a sealed tube at 165 C. for varying periods of time. This procedure is known as sealed tube `aging and represents fan aging suiiciently severe to cause marked, accelerated, progressive, permanent loss of strength. It has been found that tensile Vstrength changes which occur under sealed tube agingcQnditiQnsprOVide a highly reliable index to the heat resisting properties of the treated fibers when heat aged in rubber and plastic compositions', and therefore sealed tube aging is a valuablemethod for indicating how the treated cord will behave'when embedded in rubber in the form for example, of a tire carcass.

After the sealed tube aging period, the tensile Strength of the treatedrayon cords was determined at 70 F. and 60% relative humidity with the results shown in the following table:

Treatment of rayon tzre cord fr -n em'il stemmi ens e feng treiigtv Clfcftflighofj frime. strength compared compared iidae in treatiny so- Aged at 'of 1 to UF" t9 H1' luti'on Percen b 165 C., Treated' treated i treated,

ei hi y Hrs. Cord, Unaged 'Aged Con- W g Lbs. f Control, trol Per Percent cent 0 (Conti-01)-.-. 0 21.0 0 (Control) -7 .3.2 Y 40 o (commu. ao 0.o

0 (ControDL. 72 0.0 1 7 16.2 1 30 .0. 0 1 72 o o 3 7 19. 3 3 30 14. 4 3.. 72 0.0 5;. .7 18.8 5 30 17. 0 5.. 72 13.7 7 18. 9 30 1,6. 6 72 14.8 l 7 '17. 5 30 r5.5 72 13. 9

The results 'are also shown graphically in ljig.

1, which is aplot of thecncentration,ot2,2'-

diaminodiethylsuld in the treating solution on a hri'zqntal axisa'g A lijst vthe tehsue'st'rengupf the cord on a vertical axis, plotted for 7 hours.

30 hours, and 72 hours sealed tube heat aging.

It will be 'evidentffroni inspection dtutheutable and Fig. 1, tha'tuthe 2,`2"daminodiethylsulilde was highly maar?. migrating@ agravan cord a substantial resistance to heat deterioration. The cord treated with a 3% solutionoif the 2,2'amenagement@.retained hasta @f e5 its ri'ghal ,thsile Strength after Timers aging mid fivesioi'e. thanigtimes es, wages e Sim.- ilarly,gdiimraed-ccrq-- itwiiireaedtha there is' @Sharp risale lenslle ,Strength Qi the aged cord with irrrzreasingt concentratipns of diiliiiiethilfslflfla It will also banbte, that the optimum vconcentration advanced with `in crea'sing severity o f the aging conditions. For the less severe 7 l 1o u r ag ing test `atlfi lC., the optimum concentration was about 2 -2.5 ffgr the inore severe 72 hour test, it was about 56%.

v EXAMPLE 2y The foregoing experiment was repeated, employing gray cotton tire cord in place of rayon tire cord. The results are indicated in the fcllowing table:

Treatment of cotton tire cord l elativlela elatlzle f Tensi e trengt treng Cor-centratton of 22 Time Strength Compared Compared dlammodlethylsul' Aged at of to Unto Undt m geam 1530' 165 C., Treated treated treated u -l Bree y Hrs. Cord, Unagcd Aged Con- Welg Lbs. Control, trol, Per- Percent cent 0 (Control) 0 16. 6 0 (Control) 7 4. 9 0 (Control) 30 0. 0 (l (Control) 72 0.0 1 7 13. 2 l 30 5. 8 1 72 0. O 3 7 16. (l 3 30 l5. 4 72 13. 2 7 16. 5 30 15. 9 72 15. 2 92 7 17. 4 105 355 30 16. 7 10U 72 15. 2 92 7 1S. 0 108 367 30 16.6 100 72 15. 3 92 The results are shown graphically in Fig. 2 in the same manner as previously, and the marked improvement obtained as a result of the 2,2-diaminodiethylsulde will be evident from inspection of the table and the graph. The treated cord, after seven hours aging, was greater than two or three times as strong as the untreated cord similarly aged..

From the foregoing it is evident that the invention provides a method of treating cellulose, whether in the form of fiber such as gray cotton fibers or other forms of cellulose such as regenerated cellulose, either in the form of nonfibrous sheets, or in the form of fibers, whereby the resistance of the cellulose to the deteriorating effect of prolonged exposure to elevated temperatures is substantially enhanced. Thus, the improved cellulose articles of this invention containing a 2,2-diaminodialkylsuliide are capable of improved serviceability, especially when employed in the form of fibers for such purposes as reinforcing tires, steam hose, and similar rubber-fiber composite articles, which normally have a limited service life because of the deteriorating action of heat on the liber reinforcement therein. The 2,2'-diaminodialkylsulde treated fiber can be encased in rubber which may be subsequently vulcanized at elevated temperatures to a dense, strong product without any adverse effects due to the presence of the treating chemical. This is in contrast to certain other chemicals previously proposed for improving the heat age resistance of rayon cords and the like, but which are impracticable because they decompose at vulcanizing temperatures with a liberation of gases, causing blowing in the carcass assembly. Because the 2,2'-diaminodialkylsulfide is comparatively stable at vulcanizing temperatures it retains its chemical identity and remains in the fiber, and is available for protecting the fiber on subsequent exposure of the vulcanized articles to high temperature conditions over extended periods of service.

The 2,2diaminodialkylsulde is not decomposed or removed by temperatures ordinarily employed in drying or baking tire cord after the cord, usually in the form of a weft fabric, has been treated with rubber latex compositions.V

As indicated previously, the 2,2-diaminodialkylsulfide must actually remain as such in the cellulose and be present while the cellulose is exposed to elevated temperature service conditions in order to obtain the beneficial effects of the treatment. In this respect, my treatment differs from certain conventional treatments, particularly treatments designed to obviate the temporary, reversible loss of tensile strength observed in gray cotton fibers when heated at elevated temperatures. Such temporary loss of tensile strength occurs substantially instantaneously upon heating to elevated temperature, and the cotton regains its original strength upon cooiing to room temperature. Such temporary reversible loss of tensile strength at elevated temperature is obviated in the prior art methods referred to by removing the waxes from the native cotton, and such treatments are characterized by the fact that it is immaterial whether the treating agent is eventually removed from the cotton or whether the treating agent remains in the cotton. In contrast to this, the present invention is concerned with the slow,

progressive irreversible chemical changes which occur in cellulose, whether gray cotton containing natural waxes, or dewaxed cotton, or regenerated cellulose, induced by elevated temperatures, e. g., C. and higher. The desired protection against this form of deterioration is 0btained only if the 2,2'-diaminodialkylsuliide is:

While I have described my invention with par-- ticular reference to a preferred treatment of'.`

cellulose fibers intended to be used for reinforcing rubber articles, it will be understood that the improved 2,2-diaminodialkylsulde containing cellulose of this invention is susceptible of many other uses where resistance to heat is a desirable characteristic. However', the improved cellulose fibers of the invention are especially adapted to production of vulcanized rubber-fabric composite articles, because the 2,2'-diaminodiethylsulde has no deleterious eiect on the vulcanization, and the 2,2'-diaminodiethylsuliide resists vulcanizing temperatures, thereby resulting in improved vulcanized rubber-fabric composite articles.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The method of imp-roving the resistance of cellulose to the deteriorating eects of heat aging which comprises incorporating a water soluble 2,2'-diaminodialkylsulfide in the cellulose the said alkyl groups being lower alkyl groups containing less than seven carbon atoms.

2. The method as in claim l in which the 2,2- diarninodialkylsulde is 2,2'-diaminodiethylsul nde.

3. The method of improving the resistance of cellulose i'lbers to the deteriorating effects of heat aging which comprises impregnating the fibers with an aqueous solution of a 2,2diaminodial kylsulde the said alkyl groups being lower alkyl groups containing less than seven carbon atoms.

4. The method as 1n @mm 3v in which the fibers are gray cotton bers.

5. The method asin claim3 inv/hich-the-fibers are regenerated cellulose'bers.

6. The method as in claim 3' in which the 2,2%' diaminodialkylsuliide is 2,2-diamin'odiethylSu1-' 11de.

7. The method of improving` the resistance of gray cotton bers to the* deteriorating effects of heat agingwhich comprises imxn'ersin'gv theb'er's in an, aqueous solution of 2,2"diaminodiethyl'sul` de.

8. The method of improvingithe' resistance of regenerated cellulosebers to` the deteriorating effects ofheat aging. which compriseseimmersing the fibers in an aqueous solution-ofy 2',2f'diarnino" diethylsulfide.

9. Cellulose. containingfa Wate-rsoluble A1'2j2 -lii aminodialkylsulde the said alkyl groupsl being:

13. A regenerated lliilose fiber containing 2,2fdiaminodiethylsulda whereby the', resistance ofl the* ilber tomthe Adeteriorating effect of heet aging is, Substantially enhanced;

14. A vulcanized rubber article reinforced. with cellulose bfibers containing la Water-soluble 2,2- diaminodialkylsul'i'ide', whereby the resistance of the bers'totlfi'e deteriorating effect' of heat aging is' Jsubs taintia'llyl'.nenhanced the said alkyl groups being lower alkyl grups containing less than sei/jen"carborlatoms.xv V. Y l y 1 6. vulcanized rubber article reinforced with gray cotton bers' containing 2,2'diaminodi ethylsulfide. y V

17. A v'ulcanized rubber article reinforced with regenerated cellulose fibers containing 2,2di

lower alkyl groups. containing less` tha-ri seven; g()- aminodiethylsulflde;

carbon atoms.

10. A'cellulose ber containingafwatersoluble` 2,2 -diaminodialkylsuldedistributed throughout its structure the said:alkylgroupsbeingl lower alkyl groups containingjless--than sevencarbon-l 25';

atoms.

11. Acellulose vliber. as -in claim-.10 in which the*v 2,2'-cliaminodialkylsulde is. 2 52-diami-riodiethyb'V sulfide.

arninodiethylsuldewherebyYthe resistanceof the ber to .the deteriorating effect-of heat aging-'ris` substantiallyenhanced.-

HWARD M. BUCKWALTER.

References cited" in the nie of this patent 

1. THE METHOD OF IMPROVING THE RESISTANCE OF CELLULOSE TO THE DETERIORATING EFFECTS OF HEAT AGING WHICH COMPRISES INCORPORATING A WATER SOLUBLE 2,2-DIAMINODIALKYLSULFIDE IN THE CELLULOSE THE SAID ALKYL GROUPS BEING LOWER ALKYL GROUPS CONTAINING LESS THAN SEVEN CARBON ATOMS. 